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The difference between sleep and anaesthesia is in the intracellular signal: propofol and GABA use different subtypes of the GABAA receptor β subunit and vary in their interaction with actin
Linköping University, Department of Medicine and Care, Anaesthesiology. Linköping University, Department of Medicine and Care, Pharmacology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Care, Anaesthesiology. Linköping University, Department of Medicine and Care, Pharmacology. Linköping University, Faculty of Health Sciences.
2003 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 47, no 2, 157-164 p.Article in journal (Refereed) Published
Abstract [en]

Background: Propofol is known to interact with the γ-aminobutyric acidA (GABAA) receptor, however, activating the receptor alone is not sufficient for producing anaesthesia.

Methods: To compare propofol and GABA, their interaction with the GABAA receptor β subunit and actin were studied in three cellular fractions of cultured rat neurons using Western blot technique.

Results: Propofol tyrosine phosphorylated the GABAA receptor β2 (MW 54 and 56 kDa) and β3 (MW 57 kDa) subtypes. The increase was shown in both the cytoskeleton (β2(54) and β2(56) subtypes) and the cell membrane (β2(54) and β3 subtypes). Concurrently the 56 kDa β2 subtype was reduced in the cytosol. Propofol, but not GABA, also tyrosine phosphorylated actin in the cell membrane and cytoskeletal fraction. Without extracellular calcium available, the amount of actin decreased in the cytoskeleton, but tyrosine phosphorylation was unchanged. GABA caused increased tyrosine phosphorylation of β2(56) and β3 subtypes in the membrane and both β2 subtypes in the cytoskeleton but no cytosolic tyrosine phosphorylation.

Conclusion: The difference between propofol and GABA at the GABAA receptor was shown to take place in the membrane, where the β2(54) was increased by propofol and instead the β2(56) subtype was increased by GABA. Only propofol also tyrosine phosphorylated actin in the cell membrane and cytoskeletal fraction. This interaction between the GABAA receptor and actin might explain the difference between anaesthesia and physiological neuronal inhibition.

Place, publisher, year, edition, pages
2003. Vol. 47, no 2, 157-164 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-26816DOI: 10.1034/j.1399-6576.2003.00007.xLocal ID: 11428OAI: oai:DiVA.org:liu-26816DiVA: diva2:247366
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Cellular mechanisms of anaesthetic agents
Open this publication in new window or tab >>Cellular mechanisms of anaesthetic agents
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Anaesthesia is given to approximate 5% of the Swedish population annually, with the great advantage of painless surgery, but it also has side effects such as depression of blood pressure that might give a heart infarction. Exactly how anaesthetic agents cause anaesthesia is poorly known. Most anaesthetics have been shown to interact with the GABAA receptor, whose endogenous ligand GABA causes down-regulation of the brain and sleep. To further explore the cellular signal system used by anaesthetics this study was performed.

First, two different malignant cell lines, PC-12 and SH-SY5Y, were tested, to evaluate if they could replace animal cells; however, they did not respond with increased intracellular calcium [Ca2+]i upon stimulation with propofol, as the normal rat neurons do. This is probably due to differences in the intracellular signaling systems in these malignant cells. Therefore, the studies in this thesis were performed on rat neurons.

Propofol, an intravenous anaesthetic, was shown to cause a bicucullin insensitive increase in [Ca2+]i, where the release from intracellular stores was dependent on a tyrosine kinase. Sevoflurane, a volatile anaesthetic, also caused an ilrunediate increase in [Ca2+]i, but not nitrous oxide. Increased [Ca2+], is supposed to augment the influx of chloride ions through the GABAA receptor, hence hyperpolarising the neuron, and thereby make it anaesthetised.

Tyrosine phosphorylation of the GABAA receptor is necessary for its function. Propofol tyrosine phosphorylates another ß2 subunit in the membrane then GABA. Propofol, but not GABA, also caused a tyrosine phosphorylation of actin in both the cytoskeletal and cell membrane fraction. Together these changes might explain the difference between sleep and anaesthesia. Isoflurane, sevoflurane and nitrous oxide all tyrosine phosphmylate a protein, suggested to be the GABAA receptor ß subunit, in different cellular compartments. This might explain their different clinical effects.

Propofol and sevoflurane, but not GABA, causes actin rings to be formed in the cell, and for propofol the signal goes via rhoA and rho kinase, that also are involved in the translocation of actin to the cellular membrane. An unl~own 160 kDa protein is tyrosine phosphorylated by propofol, is part of the rho signalling pathway and is regulated by rho, This unknown protein might be involved in the actin reorganisation.

Abstract [en]

I Sverige får ca 5% av befolkningen narkos (anestesi) varje år. Narkos gör att man kan operera utan smärta, men det har också biverkningar som blodtrycksfall vilket kan ge hjärtinfarkter. Exakt varför man somnar när man sövs vet man inte, men de flesta narkosmedel binder till den mottagare (receptor) för kroppens egna nedreglerande och sömngivande ämne (GABA) som finns på nervcellens yta. För att ta reda på vad som händer i nervcellen när man sövs gjordes den här studien.

Två olika cellinjer prövades för att se om de kunder ersätta djurceller, men de svarar inte med en calciumökning när man stimulerar med narkosmedlet propofol, vilket dock nervceller från råtta gör. Det beror troligen på att cancerceller inte längre har alla signalsystem kvar. Därfår användes nervceller från friska råttor i alla försök.

Propofol, ett narkosmedel som ges i blodet, ökar mängden calcium inuti cellen. Detta sker inte genom att propofol binder till samma bindningsplats som GABA. För att släppa ut calcium från cellen inre depåer behövs ett protein, tyrosin kinas. Sevofluran (ett narkosmedel som man andas in) ger också en ökning av calcium, men inte lustgas. När calcium ökar, kommer mer negativa kloridjoner in i cellen via GABAA receptorn, och cellen somnar.

GABAA receptorn behöver tyrosin fosforyleras av ett tyrosin kinas för att öppnas för kloridjonerna. Propofol fosforylerar ß2(54) delen av receptorn när den sitter i membranet, medan GABA fosforylerar ß2(56) delen. Dessutom kan propofol, men inte GABA, tyrosinfosforylera cellskelettproteinet aktin i cellskelettet och membranet. Dessa skillnader mellan GABA och propofol kan förklara skillnaden mellan vanlig sömn och narkos. Isofluran, sevofluran och lustgas fosforylerar också ett protein som troligen är GABAA receptorn, men vart och ett av dessa narkosmedel gör det på olika ställen i cellen, vilket kan förklara varför de har olika effekter när man söver med dem.

Propofol och sevofluran, men inte GABA, gör så att aktinringar bildas i cellen. Signalen för det går via rho och rhokinas, vilka också gör så att propofol inte kan flytta aktinet från cellskelettet upp till membranet. Propofol tyrosin fosforylerar också ett okänt 160 kDa stort rho-beroende protein som troligen också är med i signalkedjan för att ändra aktinet.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2003. 89 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 777
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27461 (URN)12114 (Local ID)91-7373-536-1 (ISBN)12114 (Archive number)12114 (OAI)
Public defence
2003-03-21, Berzeliussalen, Hälsouniversitetet, Linköping, 13:00 (Swedish)
Opponent
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-09-20Bibliographically approved

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Björnström, KarinEintrei, Christina

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